Numerous polymer-based medical devices have been developed for implantation or insertion into the body. For example, in recent years, drug eluting coronary stents, which are commercially available from Boston Scientific Corp. (TAXUS and PROMUS), Johnson & Johnson (CYPHER) and others, have become the standard of care for maintaining vessel patency. These existing products are based on metallic balloon expandable stents with biostable polymer coatings, which release antiproliferative drugs at a controlled rate and total dose.
Specific examples of biostable polymers for biostable drug eluting polymer coatings include homopolymers and copolymers, such as poly(ethylene-co-vinyl acetate), poly(vinylidene fluoride-co-hexafluoropropylene) and poly(isobutylene-co-styrene), for example, poly(styrene-b-isobutylene-b-styrene triblock copolymers (SIBS), which are described in U.S. Pat. No. 6,545,097 to Pinchuk et al. FIG. 1, which is taken from Pub. No. US 2006/0171981 to Richard et al., illustrates a release profile of a stent coating that contains 25 wt % paclitaxel and 75 wt % SIBS.
Biodegradable polymers may have certain advantages over biostable polymers. For example, because they erode over time, biodegradable polymers may reduce or eliminate long term effects that may be associated with non-biodegradable polymers (e.g., foreign body effects, late stent thrombosis, etc.).